The mechanism involved in the regulation of protein and RNA synthesis during sea urchin development will be analyzed. Studies will be conducted on the activation of maternal mRNA which appears to involve two separate populations of mRNA: General mRNA, which is activated within a few minutes after fertilization and presumably depends on pH and histone, or nuclear protein mRNA that is activated 60 to 90 minutes later and seems to depend on DNA synthesis. Analysis of change in the population of mRNA during development indicates that each cell type has a set of up to a couple of hundred genes activated to produce cell-specific sets of abundant mRNA which constitute the genes involved in the differentiation of that cell type. Genes which are activated in a stage-specific manner in sea urchin embryonic development are being isolated from a genomic recombinant DNA library and will be used to study the mechanism of activation of these genes.